Regulation of liver microsomal inorganic pyrophosphate-glucose phosphotransferase, glucose-6-phosphatase and inorganic pyrophosphatase

Cloning and sequencing of the 5′ region of the human glucose‐6‐phosphatase gene: transcriptional regulation by cAMP, insulin and glucocorticoids in H4IIE hepatoma cells

“…There have been some reports in the literature ind cating that glucocorticoids (dexamethasone) increase liver g ucose-6-phosphatase enzyme activity and others showing tlat it does not (e.g. [1,12,14,[22][23][24][25][26][27]). A simple explanation fi,r these apparently conflicting findings would be that the effect of dexamethasone also depends on the levels of other h )rmones like insulin and glucagon as illustrated in Table 1.…”

A Reassessment of the Phospholipid Dependence of Membrane-Bound Enzymes, with Special Reference to GIucose-6-Phosphatase and Na+, K+-Dependent Adenosine Triphosphatase

“…The activation of the enzyme by detergents [48] occurs under conditions known to cause the removal of phospholipid from the membrane [35,50], The even more marked increase in activity observed when the enzyme is 'solubilized' by deoxycholate must be interpreted with caution, since protein as well as phospholipid is removed by the treatment and it is not possible to decide whether the enhanced specific activity is due to the enrichment of the preparation with respect to glucose-6-phosphatase or to activation of the enzyme [54,70], When phospholipid is added to a deoxycholate-solubilized preparation, under conditions which result in the formation of lipoprotein vesicles, there is a significant loss of glucose-6-phosphatase activity [54,70], Furthermore, the apparent Michaelis constant for glucose-6-phosphate (Kg6p), which can increase as much as two fold in fasted or diabetic rats, is reduced by detergent treatment to approximately the same value in control and experimental animals [49,64], Phospholipase treatment of microsomes has been shown to lower Kg6p [48,92], and the subsequent addition of phospholipid increases Kg6p-However, both the activation of glucose-6-phosphatase (based on total activity) and the lowering of Kg6p are achieved equally effectively by exposing the microsomes to high pH [3,74,75], a treatment which solubilizes some protein but does not remove phospholipid or glucose-6-phosphatase from the membrane [40], In addition, the increase in Kg6p brought about by the addition of phospholipid to phospholipiddepleted microsomes is probably not a simple reversal of the changes which caused the decrease in Kg8p during the initial treatment, since the enzyme does not appear to be restored to its original repressed form [70,92].…”

Analysis of glucose-6-phosphate translocase and hexose-6-phosphate phosphohydrolase, the two obligatory components of microsomal glucose-6-phosphatase system, in rat liver.

“…Glucose-6-phosphatase is known to respond to a variety of physiological and pathological stimuli (Nordlie et al 1968;Greengard 1971). In the present work, we have found a procedure, by which glucose-6-phosphate translocase, an obligatory component of microsomal glucose-6-phosphatase system, can be assayed with little interference by hexose-6-phosphate phosphohydrolase, another obligatory component for the system.…”

“…Glucose-6-phosphatase is also known to respond to various nutritional and hormonal stimuli (Nordlie et al 1968). Since the highest stimulation of glucose-6-phophatase observed thus far occurs in animals rendered diabetic (Jakobsson and Dallner 1968), the effect of administration of streptozotocin on the activities of glucose-6-phosphate translocase and hexose-6-phosphate phosphohydrolase were studied.…”

“…Glucose-6-phosphatase activity is known to be regulated in response to various physiological and pathological stimuli (Jakobsson and Dallner 1968;Nordlie et al 1968 ; Hanson and Nordlie 1970;Zoccoli et al 1982).. Whether the two components of the glucose-6-phosphatase system are subject to common or independent regulation has yet to be elucidated.…”